How to Make It
Light a grill. Brush the onion slices with olive oil and season with salt and pepper. Grill the onion slices and the green tomatoes over high heat, turning once, until nicely charred; about 6 minutes for the onion and 8 minutes for the tomato.
Chop the onion into 1-inch pieces and transfer to a bowl. Core, peel and coarsely chop the green tomatoes and add them to the bowl. Stir in the cilantro, red tomato, lime juice and the 2 tablespoons of olive oil. Season the salsa with salt and pepper and serve.